This invention relates to a novel method for the preparation of trialkylsulfonium, sulfoxonium, and nitrogen or phosphorus based organic quaternary salts of N-phosphonomethylglycine, compounds which are known herbicides and plant growth regulators.
Herbicides are widely used by farmers, commercial agricultural companies, and other industries in order to increase crop yields for such staple crops as corn, soybeans, rice, and the like, and to eliminate weed growth along highways, railroad rights-of-way, and other areas. Herbicides are effective in killing or controlling unwanted weeds which compete for soil nutrients with the crop plants, and by reason of the fact that they kill weeds, are responsible for improving the aesthetic appearance of highway and railroad rights-of-way. There are a number of different types of herbicides presently sold commercially, and these fall into two general categories. The categories are pre-emergence and post-emergence herbicides. The pre-emergence herbicides are applied to the soil prior to the emergence of the weed plants from the soil, and the post-emergence herbicides are applied to plant surfaces after emergence of the weeds or other unwanted plants from the soil.
One of the earliest post-emergence herbicides used commercially was 2,4-D (2,4-dichlorophenoxyacetic acid). After a number of years of use of this and similar compounds such as 2,4,5-T (2,4,5-trichlorophenoxy acetic acid), it was found that certain decomposition products of these herbicides were long lasting and were not biodegradable. While there has been some dispute between governmental agencies and commercial interests regarding the effects of residual products of 2,4-D, 2,4,5-T and similar compounds, the agencies nevertheless restricted the use of these herbicides in the United States some years ago. Since that time, efforts have been made to develop herbicides which are biodegradable into harmless residues within a relatively short time after their application.
One such compound, which has been found to be biodegradable, yet which is effective as a herbicide and plant growth regulator when employed at lower rates, is N-phosphonomethylglycine and various salts thereof. The N-phosphonomethylglycine and agriculturally effective salts have been approved for use by the U.S. Government, and, as a consequence, this herbicide has become extremely successful commercially.
The N-phosphonomethylglycine and certain salts are the only effective and approved post-emergence herbicides in the field. The present commercial compound is the isopropylamine salt of N-phosphonomethylglycine and derivatives thereof. In field use it is normally applied in amounts of from 0.01 to about 20 pounds per acre, preferably from 2 to 6 pounds per acre.
The N-phosphonomethylglycines, and certain soluble salts thereof, can be made in a number of different ways. One such method, as described in U.S. Pat. No. 3,160,632 (Toy et al., Dec. 8, 1964) is to react N-phosphinomethylglycine (glycinemethylenephosphinic acid) with mercuric chloride in a water solvent at reflux temperature, and subsequently separating the reaction products. Another method is the reaction of ethyl glycinate with formaldehyde and diethylphosphite. The latter method is described in U.S. Pat. No. 3,799,758 (Franz, Mar. 26, 1974). In addition, there is a whole series of patents, relating to N-phosphonomethylglycines, their salts, and derivatives thereof, described as being useful herbicides and plant growth regulators. Such additional patents relating to the N-phosphonomethylglycines, methods of application, methods of preparation, salts, and derivatives, include U.S. Pat. No. 3,868,407, U.S. Pat. No. 4,197,254, and U.S. Pat. No. 4,199,354, among others.
The trialkylsulfonium and sulfoxonium salts of N-phosphonomethylglycine have also been found to be useful as plant growth regulators and herbicides. These salts are described in U.S. Pat. No. 4,315,765, Large. As disclosed in that patent, the compounds can be prepared from N-phosphonomethylglycine by reacting the latter with silver oxide to form the silver salts or with sodium hydroxide to form the sodium salt, and treating either the silver or sodium salt with a trialkylsulfonium or sulfoxonium halide. It is desirable to simplify this process to make it unnecessary to isolate intermediate products, and the process of the presant invention is directed to that end in order to simplify and make less expensive the process for the production of the sulfonium and sulfoxonium salts, and for certain nitrogen or phosphorus based organic quaternary salts.